Add some sand, and just go with it. I toss in a bit of scratch to our (bare dirt/sand) run every morning, and occassionally give the hens some kitchen scrap greens or some such as a treat. Unless your run is huge, or you are able to rotate chicken 'pastures', you will not be able to maintain vegetation in it. Your coop/aviary is beautiful, by the way. Very nice work!
We found it works great to till the run once in a while. After a period of time it gets packed down and the poo just stays there. ( we don't get alot of moisture like some areas of the country, at least not until the snow gets 5 feet deep!) Tilling stirs up fresh bugs and other goodies and allows them to dust bath too.
